Study On Hydrodynamic Characteristics Of Annulus Cavitation Device And Numerical Simulation

Hydrodynamic cavitation is a process that vapor or bubble between the liquid interior or liquid-solid interface are formed,developed and collapsed,when the partial pressure within the liquid is lower than the saturated vapor pressure of the liquid.Bubble collapse will produce high temperature,high pressure and high-speed micro-jet and other extreme physical conditions.The energy released in hydrodynamic cavitation can be used in wastewater treatment and enhance some chemical reaction.This dissertation studied a kind of annulus cavitation device with the bluff body,compared with the conventional venture tube and orifice plate device,the annulus cavitation device can greatly improve the processing capacity and increase the cavitation area.The rapid development of computational fluid dynamic(CFD)technology provides a new way for people to study hydraulics.In this thesis,the CFD software FLUENT is used to simulate the flow fields of cavitation in the annulus cavitation device.The influences of structural parameters and operation parameters and physical characters on cavitation effect are investigated,and the shape of the shaft is also optimized.In addition,the influence of the structural parameters of the annulus cavitation device with the two-stage bluff body on cavitation effect is analyzed,and some conclusions are educed.(1)The different types of inner shaft have a significant influence on the range of high vapor volume fraction,and the spherical inner shaft device has the highest vapor volume fraction range.(2)The optimization of the annulus cavitation device could significantly improve the cavitation effect,and the optimized cone-shaped inner shaft device could produce the strongest cavitation effect.(3)The value of the annulus rate has a great influence on cavitation effect.In this study the cavitation model with annulus rate ?=0.28 has the strongest cavitation effect.(4)The external cavity with the expansive type could improve the cavitation effect,but the external cavity with the contractile type could debase cavitation effect.(5)When inlet pressure is constant,increasing back pressure can cause the inhibition of the cavitation effect.The increase of the fluid temperature could enhance cavitation effect.The increase of the wall roughness is not conducive to cavitation effect.When the gas dissolved in the liquid is very little,cavitation effect enhances along with the increasing of the gas.And when the gas increases to some degree,cavitation effect weakens along with the increasing of the gas.(6)For the two-stage annulus cavitation device,the spacing and the maximum diameter of two stage bluff bodies have an important influence on the cavitation effect.When the spacing between the bluff bodies is too far or too close,the cavitation effect will be weakened;when the maximum diameter of the first stage bluff body is large than the second stage bluff body,the two-stage annulus cavitation device could produce strong cavitation phenomenon.